1. Technical Field
A method of forming a gate in a semiconductor device, is disclosed which can prevent abnormal oxidization and lifting at an interface of the stack gate which comprises polysilicon and a metal. The disclosed method can be applied to even the single metal gate, by replacing a re-oxidization process for reducing damage to the gate oxide film generated during the gate patterning process with an oxygen plasma treatment.
2. Background of the Related Art
In the conventional process of forming a gate electrode using a polysilicon film, a re-oxidization process is performed for the purpose of reducing micro-trench damage occurring in the gate oxide film when the polysilicon film is etched and for increasing the device reliability by oxidizing the electrode material remaining in the semiconductor substrate and increasing the thickness of the gate oxide film at the gate edge. It is important to perform the re-oxidization process since the thickness and film quality of the gate oxide film at the gate edge significantly influences hot carrier properties, sub-threshold properties (off-leakage, GIIDL, etc.), punch-through properties, the operation speed of the device, reliability, and the like.
In recent years, in order to lower the resistance of the gate, the polysilicon film and the metal film are stacked to form the gate. The stack structure of the polysilicon film and the metal film, however, has such problems as rapid dimension expansion; or an increase in the surface resistance, or related problems caused during a subsequent high temperature annealing process or the oxidization process. In particular, the most significant problem in the process is that lifting occurs since the metal film is oxidized in a given oxidization atmosphere. A new process that was developed in order to overcome this problem is the selective oxidization process. In other words, in the selective oxidation process, the metal film is not oxidized but only the polysilicon film and the semiconductor substrate are oxidized, in a hydrogen (H2) rich oxidization atmosphere. However, the current selective oxidization process has a problem in that it is possible when the tungsten film or the tungsten nitride film is used as the metal gate electrode. Further, as this oxidization process is possible in the H2 rich atmosphere and at a very high temperature of 700° C., it may have influence on the characteristic of the MOSFET device.